Observation of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Y</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mn>4230</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math> and evidence for a new vector charmoniumlike state <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Y</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mn>4710</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math> in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>e</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:msup><mml:mi>e</mml:mi><mml:mo>−</mml:mo></mml:msup><mml:mo stretchy="false">→</mml:mo><mml:msubsup><mml:mi>K</mml:mi><mml:mi>S</mml:mi><mml:mn>0</mml:mn></mml:msubsup><mml:msubsup><mml:mi>K</mml:mi><mml:mi>S</mml:mi><mml:mn>0</mml:mn></mml:msubsup><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:math>
M. Ablikim, М. Н. Ачасов, P. Adlarson, M. Albrecht, R. Aliberti, A. Amoroso, M. R. An, Q. An, Xiaoshuan Bai, Y. Bai, O. Bakina, R. Baldini Ferroli, I. Balossino, Y. Ban, V. Batozskaya, D. Becker, K. Begzsuren, N. Berger, M. Bertani, D. Bettoni, F. Bianchi, J. Bloms, A. Bortone, I. Boyko, R. A. Briere, A. Brueggemann, H. Cai, X. Cai, A. Calcaterra, G. F. Cao, N. Cao, S. A. Çetin, J. F. Chang, W. L. Chang, G. Chelkov, C. Chen, Chao Chen, G. Chen, S. Chen, M. L. Chen, S. J. Chen, Shaomin Chen, T. Chen, X. R. Chen, X. T. Chen, Y. B. Chen, Z. J. Chen, W. S. Cheng, S. K. Choi, X. Chu, G. Cibinetto, F. Cossio, J. J. Cui, H. L. Dai, J. P. Dai, A. Dbeyssi, R. E. de Boer, Dmitri Dedovich, Z. Y. Deng, A. Denig, I. Denysenko, M. Destefanis, F. De Mori, Y. Ding, J. Dong, L. Y. Dong, M. Y. Dong, X. Dong, S. X. Du, P. Egorov, Y. L. Fan, J. Fang, S. S. Fang, W. X. Fang, Y. Fang, R. Farinelli, L. Fava, F. Feldbauer, G. Felici, C. Q. Feng, J. H. Feng, Kamil Leszek Fischer, M. Fritsch, C. Fritzsch, C. D. Fu, Han Gao, Y. N. Gao, Yang Gao, S. Garbolino, I. Garzia, P. T. Ge, Z. W. Ge, C. Geng, E. M. Gersabeck, A. Gilman, K. Goetzen, L. Gong, W. X. Gong, W. Gradl, M. Greco
Abstract
Cross sections for the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{K}_{S}^{0}{K}_{S}^{0}J/\ensuremath{\psi}$ at center-of-mass energies from 4.128 to 4.950 GeV are measured using data samples with a total integrated luminosity of $21.2\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ collected by the BESIII detector operating at the BEPCII storage ring. The $Y(4230)$ state is observed in the energy dependence of the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{K}_{S}^{0}{K}_{S}^{0}J/\ensuremath{\psi}$ cross section for the first time with a statistical significance of $26.0\ensuremath{\sigma}$. In addition, an enhancement around 4.710 GeV, labeled as the $Y(4710)$, is seen with a statistical significance of $4.2\ensuremath{\sigma}$. There is no clear structure around 4.484 GeV. Using a fit with a coherent sum of three Breit-Wigner functions, we determine the mass and width of the $Y(4230)$ state to be $4226.9\ifmmode\pm\else\textpm\fi{}6.6\ifmmode\pm\else\textpm\fi{}22.0\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ and $71.7\ifmmode\pm\else\textpm\fi{}16.2\ifmmode\pm\else\textpm\fi{}32.8\text{ }\text{ }\mathrm{MeV}$, respectively, and the mass and width of the $Y(4710)$ state to be $4704.0\ifmmode\pm\else\textpm\fi{}52.3\ifmmode\pm\else\textpm\fi{}69.5\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ and $183.2\ifmmode\pm\else\textpm\fi{}114.0\ifmmode\pm\else\textpm\fi{}96.1\text{ }\text{ }\mathrm{MeV}$, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the average Born cross section ratio $\frac{{\ensuremath{\sigma}}^{\text{Born}}({e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{K}_{S}^{0}{K}_{S}^{0}J/\ensuremath{\psi})}{{\ensuremath{\sigma}}^{\text{Born}}({e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}J/\ensuremath{\psi})}$ is measured to be ${0.388}_{\ensuremath{-}0.028}^{+0.035}\ifmmode\pm\else\textpm\fi{}0.016$, or ${0.426}_{\ensuremath{-}0.031}^{+0.038}\ifmmode\pm\else\textpm\fi{}0.018$ if three-body phase space is considered.